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Lignocellulosic fiber reinforced composites: influence of compounding conditions on defibrization and mechanical
properties
Johnny Beaugrand, Françoise Berzin
To cite this version:
Johnny Beaugrand, Françoise Berzin. Lignocellulosic fiber reinforced composites: influence of com- pounding conditions on defibrization and mechanical properties. Journal of Applied Polymer Science, Wiley, 2013, 128 (2), pp.1227-1238. �10.1002/app.38468�. �hal-01267981�
A L I M E N T A T I O N A G R I C U L T U R E
Impact of thermo-hydro environment and specific mechanical energy on defibring
using flow modelling and extrusion
Johnny BEAUGRAND, Françoise BERZIN
INRA, FARE research unit, Reims, France
(Fractionation of lignocellulosic resources and Environment )
1
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Lignocelluloses defibring
Transformation
Compound/Composite material + Polymer matrix
2
Extrusion
Wood / long fibres
final composite properties = f (initial fibre quality & comportment under processing conditions)
We know :
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Aspect ratio ‘L/W’ and size influence composite end uses properties
Extrusion
L w
Compound/Composite material Aspect ratio ‘L/W’
And Fragmentation
3
Bundles
Elementary fibres Fragment particles
Individualisation
Lignocellulosic fibres
We know
Lignocelluloses defibring
Is it possible to control the defibring in order to enhance the mechanical properties of composites?
Δ Distribution profile
:
L W
Bundles
Elementary fibres
Fragment particles
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Control of the defibring : hypothesis about fibre’ ruptures
locations?
‘Anatomical defects’
Polymer Mobility (Tg)
cm mm µm nm
Inter fibres (individualisation) Intra fibres (fragmentation)
origins?
Theorical L/W or
Theorical material
reinforcement or
decohesion dammage
Structure
4
A L I M E N T A T I O N
A G R I C U L T U R E 5
Macroscopic impact
Rupture location
First strategy : playing on fiber polymer mobility
From Salmén and Olsson 1998
9.0%
14.0
%
22.5
%
3 fibre moisture contents
2 extrusion temperatures
100 °C 140 °C
‘glassy’
‘rubbery’
H
2O
T °C
Glass transition Tg
lignins
hemicelluloses
Lignins
Hemicelluloses
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
6
Second strategy : playing on extrusion process
Taken from glass fibre
SME Specific Mechanical Energy (kWh/t)
0 500 1000 1500 2000 2500 3000 3500 4000
0 100 200 300 400 500 600 700
Average length (µm)
Specific mechanical energy SME (kWh/t) internal
mixer
laboratory scale extruder
industrial scale extruder
[
0] ( )
( ) exp '
L t
n= L − L
∞− k SME + L
∞1
max max
N C
SME r W
Q N C
=
Where:
Q is the mass feed rate, N is the screw speed,
Nmax the maximum screw speed (680 rpm), r the motor efficiency (0.93),
C the torque,
Cmax the maximum torque, W the nominal power (9.2 kW)
intensity of the thermomechanical treatment
Transposable to natural fibres?
6
A L I M E N T A T I O N A G R I C U L T U R E
Materials
ε-caprolactone T
melting: 60°C – M
w: 80.000 g/mol Hemp bast fibre 20 % (w/v) 2 cm length on average
Materials and methods
Extrusion
Laboratory scale twin-screw extruder (Clextral BC 21)
Simulation/modeling of the fibre’ thermomechanical history
Trials
Compounding caprolactone / fibres in different conditions Analyze of fiber L/W in compounds
Analyze of mechanical properties Young modulus and Yield
max(tensile tests)
7
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
LUDOVIC
©: global model based on mass and thermal balance equations allowing to calculate the principal flow parameters
Vergnes et al., Polym. Eng. Sci., 1998
Pressure
Shear rate
Temperature
Residence time
Filling ratio…
Screw Die
Temperature
Pressure
Residence time
Twin-screw extrusion modeling software
8
A L I M E N T A T I O N A G R I C U L T U R E
Screw profile 1
‘hard’
Screw profile 2
’soft’
Study of formulation (at constant screw speed 250 rpm and feed rate 0.85 kg/h)
Influence of fibre water content: 9 – 14 – 23 (%)
Influence of temperature: 100 – 140 (°C)
Study of extrusion conditions (at constant humidity 50% and temperature 100°C)
Influence of screw speed: 100 - 200 - 300 - 400 (rpm)
Influence of feed rate: 0.85 – 1.5 (kg/h)
Caprolactone + Fibres
Caprolactone Fibres
Extrusions set up
9
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Fibres morphology (L/W)
Sampling zones
Optical Image Analysis
Fibres elements L/W
Characterization – Extruded hemp fibres
10
A L I M E N T A T I O N A G R I C U L T U R E
0 200 400 600 800 1000 1200 1400
0 400 800 1200 1600 2000
Calculated SME (kWh/t)
Measured SME (kWh/t) Total
After fibre introduction
o Computation of the total SME and SME received by fibers
Results: effects of extrusion conditions
Slight underestimation of SME calculated by LUDOVIC
© 11Screw profile 2
Only
Good fitting of experimental and simulated SME for total energy
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
o Effects of screw speed and feed rate (profile 2)
SME if screw speed
SME if feed rate
Results: conditions of twin-screw extrusion
200 400 600 800 1000 1200 1400 1600 1800
100 200 300 400
SME (kWh/t)
Screw speed (rpm) 0.85 kg/h
1.5 kg/h a)
12
A L I M E N T A T I O N A G R I C U L T U R E
o Effects of formulation (profile 1, 250 rpm, 0.85 kg/h)
Fibres water content L/W
Extrusion temperature L/W
Results: characterization of fibres
13
14 16 18 20 22 24 26 28
8 10 12 14 16 18 20 22 24 Water content (%)
Fibre aspect ratio (-)
b)
100°C
140°C
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
o Effects of extrusion conditions (profile 2)
Screw speed L/W ≈
Feed rate L/W
Results: characterization of fibres
14
20 25 30 35 40 45
100 200 300 400
Fibre aspect ratio (−)
Screw speed (rpm) 1.5 kg/h
0.85 kg/h b)
A L I M E N T A T I O N A G R I C U L T U R E
o Effects of SME
L = L
∞+ (L
0– L
∞) exp (-K.SME)
L
0= 2000 mm, L
∞= 400 mm and K = 0.003 (kWh/t)
-1 L and L/W with SME
L and L/W with profile 1
0 200 400 600 800 1000 1200 1400 1600
0 500 1000 1500 2000
SME (kWh/t) Fibre length (µm) Profile 2
Profile 1
0 5 10 15 20 25 30 35 40
0 500 1000 1500 2000
Fibre aspect ratio (−)
SME (kWh/t)
Profile 1 Profile 2
Results: influence of extrusion conditions
15
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
o Effects of formulation (profile 1, 250 rpm, 0.85 kg/h)
Water content Stress and Young modulus at 100 ° C
Different behavior at 140 ° C
Results: mechanical properties
16
30 32 34 36 38 40 42 44
8 10 12 14 16 18 20 22 24 Water content (%)
a)
Stress at break (MPa)
100°C
140°C
210 220 230 240 250 260 270 280
8 10 12 14 16 18 20 22 24
Young modulus (MPa)
Water content (%) b)
100°C 140°C
A L I M E N T A T I O N A G R I C U L T U R E
o Effects of fiber aspect ratio (profile 1, 250 rpm, 0.85 kg/h)
Aspect ratio Stress and Young modulus
Influence of temperature
Results: mechanical properties
17
30 32 34 36 38 40 42 44
14 16 18 20 22 24 26 28
Stress at break (MPa)
Fibre aspect ratio (-) 100°C
140°C a)
210 220 230 240 250 260 270 280
14 16 18 20 22 24 26 28
Young modulus (MPa)
Fibre aspect ratio (-) 100°C 140°C
b)
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
o Effects of extrusion conditions (profile 2)
Low or no effect of screw speed
Feed rate Stress and Young modulus
Results: mechanical properties
18
20 22 24 26 28 30 32
100 200 300 400
1.5 kg/h
0.85 kg/h
Screw speed (rpm)
Stress at break (MPa)
a)
140 160 180 200 220 240 260 280
100 200 300 400
1.5 kg/h
0.85 kg/h
Screw speed (rpm)
Young modulus (MPa)
b)
A L I M E N T A T I O N A G R I C U L T U R E
o Effects of fibre aspect ratio (profile 2)
Mechanical properties (stress at break and Young modulus) are affected by L/W
Results: mechanical properties
19
20 22 24 26 28 30 32
26 28 30 32 34 36 38
0.85 kg/h
1.5 kg/h a)
Fibre aspect ratio (-)
Stress at break (MPa)
140 160 180 200 220 240 260 280
26 28 30 32 34 36 38
0.85 kg/h
1.5 kg/h b)
Fibre aspect ratio (-)
Young modulus (MPa)
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
o Effects of fibre aspect ratio (profiles 1 and 2)
No identical properties between screw profiles 1 & 2
Results: properties – morphology correlation
20
10 15 20 25 30 35 40 45
10 15 20 25 30 35 40
Profile 1
Profile 2 a)
Fibre aspect ratio (-)
Stress at break (MPa)
140 160 180 200 220 240 260 280 300
10 15 20 25 30 35 40
Profile 1
Profile 2 b)
Fibre aspect ratio (-)
Young modulus (MPa)
Problem: at identical L/W ratio ≠ material properties
A L I M E N T A T I O N A G R I C U L T U R E
Yes, partial control of the defibring can be done
and useful for mechanical properties enhancement - Fiber defibring depends on extrusion conditions
(rotation speed and feed rate) through SME
- To favour L/W: twin-screw extrusion at high feed rate (low SME) as for glass fiber (limit breakages)
No simple relation between L/W and mechanical properties: other influences (size and fibre adhesion...)
Conclusions
21
Is it possible to control the defibring in order to enhance the
mechanical properties of composites?
A L I M E N T A T I O N A G R I C U L T U R E
E N V I R O N N E M E N T
Contacts:
Physical and chemical transformations of lignocelluloses (fibres and composites):
http://www.lille.inra.fr
[email protected] [email protected]
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